The present invention relates to flexible packaging containers that are made of plastic.
Plastic packagings are characterized in that they are light, stable, relatively tight, more particularly watertight and airtight and, at the same time, cost-effective. For that reason, they are extensively used for the packaging of free-flowing solids in a great number of fields, such as, for example, in the chemical industry (granulates, etc.), in the gardening business (garden soil, fertilizers), and in the food trade.
For cost reasons, preferred use is made of so-called FFS tubes (Form-Fill-Seal). In this instance, the packaging container is made of a endless film web, in most cases immediately before the filling phase. The endless film web is either manufactured as a tube, or a tube is initially formed from a flat film or sheet by being folded over and sealed or glued in the longitudinal direction. The tube is delivered to the filling unit where a first sealed or glued transverse seam forms the bottom and, after the product has been filled in, the container is closed at its top by a second sealed or glued seam extending in the transverse direction.
When building materials which are often hygroscopic are packaged, the protection of the contents from moisture is of particular importance. On the other hand, such products are still very often filled in paper containers, because cement and similar materials, while and after they are filled, are particularly apt to develop an overpressure in the packaging. This overpressure may escape through paper, but remains inside the airtight type of plastic packaging, after these are closed and sealed.
To avoid these problems, it is a known practice to provide a valve in the bottom of so-called block bottom bags, with the overpressure being relieved through the valve during filling. For cost reasons, however, block bottom bags and, more particularly, block bottom bags with expensive and complicated valve designs are not preferred for comparatively low-cost products, such as building materials.
EP 444 261 describes flexible packaging containers in the form of a sack or bag where overpressure relief is achieved by means of perforations in a region of the container where the latter comprises two layers. To this end, perforations are provided both in the interior wall and the exterior wall, wherein the perforations in the exterior wall should have a smaller cross-sectional area than the perforations in the interior wall. Deflation is then achieved by an overpressure developing between the interior and exterior walls, such that the overpressure is intended to permit a controlled escape. The publication discloses that, when products are very fine, a filter is required between the interior and exterior walls, in order to prevent the product from escaping. Furthermore, these perforations, which are arranged immediately one above the other after the overpressure has been relieved, form an opening for entry of air, water and other contaminants.
There is, hence, still a demand for a low-cost packaging container that can, at the same time, reliably protect products from contamination and/or moisture when overpressure must be relieved during and/or after said products are filled in.